It recently got easier to build code-compliant masonry fireplaces and chimneys. The new International Residential Code (IRC) is better written and easier to understand. There isn't any reason to rely on a proprietary or listed system because the new code is no longer confusing. Any mason, builder, or building official can easily understand it.
Masonry fireplace and chimney construction are regulated by the building code. Unlike UL or some other “listing,” the building code is not proprietary. The sections which regulate residential construction are “prescriptive” so that they can be understood and followed by a contractor or craftsman without needing to hire an engineer.
The several “model codes” formerly used in the United States (BOCA, NFPA, UBC, SBCCI, and One and Two Family) have been merged into one new International Building Code (IBC) and its residential counterpart, IRC. This development has been a major ten-year effort. The part regulating fireplaces and chimneys is in Chapter 10.
In addition to the building codes, most states, some local jurisdictions, and occasionally the federal government, sometime adopt or enact various energy, indoor air quality, and emissions regulations, all of which are generally enforced by the building official.
The IRC is usually better than any of the old model codes that it replaced. It's more logically organized, more integrated with the rest of the code, and more clear on long-confusing issues, such as clearance to combustibles and flue lining installation. It's a better code for masonry because masons, builders, and code officials can more easily understand and apply it.
This article outlines two of the most important features of the IRC –clearances to combustibles and clay flue lining installation. Other important issues, such as smoke chamber wall thickness, referencing of many ASTM standards, and a complete rewrite of the seismic design sections, are not included because of space considerations.
Since there are many changes, it's more important than ever to get a current copy of the IRC and read it. All is not the way it used to be.
Clearances to combustibles